Reading some of these stories gives the feeling of wearing unfamiliar bifocals, needing to angle the head awkwardly so as to bring the fields of vision into alignment. Alice Munro starts with stories that are embroiderings of her family's history, then follows them with more personal pieces, where details are freely changed, but faith is kept with a core of memoir.

The historical background of the Laidlaws, Munro's forebears, is even more erratic in its alternation of fullness and blanks than might be expected. Writer James Hogg was a relative, so that when James Laidlaw, having emigrated from Scotland to Canada with several of his grown children, wrote to one who had stayed behind, the letter was printed in full in Blackwood's Magazine, to the great annoyance of the man who wrote it. A number of relatives kept journals and, late in life, Munro's father, Rob, wrote not only fragments of memoir but a novel.

The past needs interpreting even when it is documented. What Spartan arrangement, exactly, was Rob Laidlaw referring to so drily with the sentence: 'We never washed any dishes and had a new plate every meal?' They didn't have as much as a table.

'When you write about real people,' Munro remarks, 'you are always up against contradictions.' I'm not sure that's the problem: fiction thrives on contradictions. Life, though, is amateurish in its shaping. More fates fizzle than explode. People make false starts and die arbitrary deaths. Munro's filling of the gaps is lovely in itself, but keeps bumping up against the implacability of the record.

Her psychology is rich even when the lives described are bare. The severity of conditions in Canada was a good fit with the religious expectations of the immigrants. As Munro puts it, they 'constructed a life for themselves that was monastic without any visitations of grace or moments of transcendence'. Four sisters can live in a house without a mirror between them (their brothers have one for shaving), relying on each other to confirm that they're adequately turned out.

In one passage, Munro refers to the 'glacial geography' of Canada and the existence of maps that show how the Ice Ages shaped the landscape. She is undertaking something similar on the level of culture, charting the remains and the permanent scouring effects of the retreating glacier known as Presbyterianism.

The stories in the second half of The View From Castle Rock revolve around a version of Munro herself. She has freely altered other characters, who joined the Salvation Army or 'revealed that they had once lived in Chicago. One of them got himself electrocuted and another fired off a gun in a barn full of horses'. The benefit of this constrained freedom is clear from the first such story, 'Fathers'. Munro has never been afraid to tamper with the formula of the well-made. Here, she interrupts what seems an urgent narrative, about a girl raging against her violent father, with a much more low-key reminiscence of having supper with the parents of a school acquaintance. The real story is the beginnings of Munro's character as a writer, in her search for the common element in the relationships she sees and the one she experiences with her father.

The pattern recurs in 'The Ticket': 'I had three marriages to study, up close, in this early part of my life.' Her parents weren't well matched but made a go of things as a couple and in a business in the hard days after the war, when the mother became an effective saleswoman for silver fox scarfs and capes made from animals that the father bred. Then her health broke down with Parkinson's disease.

Munro's paternal grandparents were a more complicated case, her grandmother being an Anglican tomboy who turned herself into a silent farmer's Presbyterian housewife, with a thoroughness not really borne of conviction: 'Not to have anybody say that she regretted a decision that she had made, or wanted anything that she couldn't have.'

The anomalies were Munro's Great Aunt Charlie and Uncle Leo. Everyone could see they were 'fond of each other'. 'I believe now,' Munro writes, 'that there was harmony, a flow of satisfaction between them, brightening the air around so that even a self-centred child could be aware of it.'

Not everybody agrees with Philip Roth that a family is doomed when a writer is born into it, but even without a conscious settling of accounts, family members can be lacerated by the passing of a powerful pen. It's not that Munro's judgments are harsh - they're not - and her verdict on her younger self is far from indulgent. But the rules of engagement with reality seem to change from story to story.

In one, when she accompanies her father to hospital and is asked his age, she answers: '52', missing the mark by two decades. What she has given is 'the age of a man I am in love with'. There are no further details given, but the artificially offhand phrase has an odd resonance. 'A' man, not 'the' man? It is as if she is reserving the right to be in love with others, at the same time or another. In the stories nearer the present, she has a husband, who isn't described or named, though a flow of satisfaction is implied.

These are minor distractions of focus, but there is a shock for the reader in the story 'Home'. A stepmother called Irlma, owner of a flatulent old dog, a stout and hilarious person with a confrontational side, which is put down to Irish ancestry and having been born on a train.

A stepmother! You've been keeping that awfully quiet. Again, it's not that the rendering of the relationship is anything but exquisite, particularly the thought that her father seems a little strained in the company of his daughter and second wife, 'as if it took some energy explaining and defending us, one to the other'. And perhaps the character has been transformed or made up out of whole cloth. It seems most likely, though, that death has closed one mouth and made possible the unsealing of another.